This invention relates to energy absorber systems and, more particularly, to energy absorbing vehicle bumper systems.
Bumpers typically extend widthwise across the front and rear of a vehicle and are mounted to rails which extend in a lengthwise direction. Desirable energy absorbing bumper systems minimize vehicle damage by managing the impact energy of a collision with a minimal amount of intrusion while not exceeding the rail load limit of the vehicle. The ideal energy absorber achieves high efficiency by building load quickly to just under the rail load limit and maintains that load constant until the impact energy has been dissipated.
U.S. Pat. No. 4,762,352 to Kaisha describes an energy absorbing bumper system. According to this patent, a foam type resin of polypropylene, polyurethane or the like is positioned between the backup beam and an outer fascia to form an assembly.
Another foam type energy absorbing bumper system is described in U.S. Pat. No. 4,941,701 to Loren. According to this patent, a semi-rigid resilient fascia is spaced forwardly of the bumper structure and the volume defined therebetween is filled with an integral skin urethane foam that is resiliently deformable and integrally bonded to both members.
Disadvantages of foam type systems include slow loading upon impact which results in a high displacement. Typically, foams are effective to a sixty or seventy percent compression. Beyond this point, foams become incompressible so that the impact energy is not fully absorbed. The remaining impact energy is absorbed through deformation of the backup beam and/or vehicle structure. Foams are also temperature sensitive so that displacement and impact absorption behavior can change substantially with temperature. Typically, as temperature is lowered, foam becomes more rigid, resulting in higher loads. Conversely, as temperature rises, foams become more compliant resulting in higher displacements and possible vehicle damage.
U.S. Pat. No. 4,533,166 to Stokes describes non-foam energy absorbing system using a channel section shaped inner beam positioned inside a contoured outer beam having a channel shaped cross section. The outer beam has transverse ribs stiffening the vertical portion with longitudinal stiffeners running between the ribs. The inner beam has transverse interbeam support sections molded in the exterior sides of the beam. Interbeam supports are positioned longitudinally displaced from the bumper supports to affix the outer beam member to the inner beam member in spaced apart relationship. The double beam bumper is designed to be relatively insensitive to the location of the point of impact as far as energy absorption and impact forces are concerned with the purpose of eliminating bumper shock absorbers. The system requires separately molded outer beam and inner beam members having a particular shape.
The present invention is directed to an energy absorbing system of the non-foam type which is designed to achieve fast loading and efficient energy absorption upon impact. Impact forces during low speed impacts are maintained just below a predetermined level by deforming the energy absorber until the kinetic energy of the impact event has been absorbed. Once the impact is over, the absorber returns substantially to its original shape and retains sufficient integrity to withstand subsequent impacts.
The energy absorbing system of the present invention has a configuration which promotes superior energy absorption efficiency and fast loading. The configuration permits the system to be packaged into a relatively small space compared to conventional foam systems. This gives automotive designers the freedom to style bumper systems with reduced overhang while enhancing the impact performance of the system. Enhanced bumper impact performance translates to reduced costs of repair for low speed xe2x80x9cfender bendersxe2x80x9d and greater occupant safety during higher speed collisions. Since the primary absorbing system can be achieved with a unitary and integrally molded thermoplastic engineering resin, the primary energy absorbing system can be easily recycled. Since foam is not utilized, greater consistency of impact performance may be achieved over varied temperatures. Another desirable characteristic of the invention is a smooth, predictable, loading response essentially regardless of load direction. This is especially important for front energy absorbing applications where consistent bumper system response is important to crash severity sensors.
In accordance with the preferred embodiment of the present invention, there is provided a unitary elongated energy absorber adapted for attachment to a vehicle, said energy absorber comprising a flanged frame for attachment to said vehicle and a body extending from said frame, said body including a first transverse wall, a second transverse wall spaced from said first wall and a plurality of tunable crush boxes extending therebetween.
Also in accordance with the present invention, the energy absorber is provided as a unitary and integral molded thermoplastic part which is adapted for attachment.